Host cell components which become associated with animal viruses during virus replication may possess altered immunological properties. The immunogenicity of murine tumor cell components, for example, is greatly enhanced by their association with oncolytic viruses. Normal and malignant mouse cells will be infected with representative enveloped and "naked" viruses. The progeny viruses will be studied for their ability to induce anti-cellular and anti-tumor immune responses in inbred strains of mice. Virus-induced immune responses will be compared to those obtained by immunization with whole cells, cell extracts, membrane fractions, and isolated surface antigens. Viruses which elicit anti-cellular as well as anti-viral responses will be studied to determine the dependence of these responses on a functional thymus-derived lymphocyte population in the immunized animal. The objectives of this research are: 1. To clarify the nature of the association between selected enveloped and "naked" viruses and host cell antigens in a model where the immunogenicity of such antigens is enhanced. 2. To determine whether any cellular antigens of methylcholanthrene-induced tumors, lymphocytes, or thymocytes become associated with infecting viruses. 3. To determine whether the immunogenicity of these is enhanced by their association with the infecting virus. 4. To determine whether the cellular requirement for an immune response to such virus-associated cellular antigens is different from that of the cell bound or extracted antigen.